Screw-threaded bottle closures



NOV. 25, 1969 11g, EVANS ETAL 3,480,170

scREw-THREAQED BOTTLE cLosUREs Filed 061'.. 1, 1968 2 Sheets-Sheet 1 inventori 'V G EVANS Bg. A. RYbER .gwbw Ms Norneyg Nov. 25, 1969 T. G. EVANS ETAL SCREW-THREADED BOTTLE CLOSURES 2 Sheets-Sheet 2 Filed Oct. l, 1968 United States Patent O U.S. Cl. 21S-43 6 Claims ABSTRACT F THE DISCLOSURE A screw-threaded closure cap for a container or the part of the container onto which the cap is screwed is provided with a screw-thread having a thread profile with a step in that flank of the thread which trails as the thread is screwed up. When the stepped thread is provided on the cap, the container has a cooperating thread of conventional profile and conversely when the stepped thread is provided on the container, the cap has a cooperating thread of conventional prole. When the cap is screwed on to the container, the crest of the conventional thread has a clearance at the root of the stepped thread and the step is so shaped that as the two threads are tightened and there is an axial thrust between them, the crest of the conventional thread is forced onto the step which has an interference t with the crest of the conventional thread so that the cap is frictionally held tightly against release on the container.

This invention relates to screw-threads which have a self-locking characteristic for making screw-threaded container closures self-locking in such a way that so great a torque is necessary to unscrew the closure that a child would find it more diicult to open than an ordinary screw cap. The invention is therefore particularly useful in connection with containers for pharmaceutical or other dangerous substances which are commonly found in the home but which must be kept away from children.

The aim of the present invention is to provide a selflocking screw-thread which can be constructed in such a way that the torque which resists unscrewing persists even after the thread has been unscrewed to a small extent. Further, the thread can be manufactured by a mouldingr technique without very close tolerances being required and it can be applied to moulded parts of small wall thickness which can'be cheaply manufactured.

According to this invention, a container or closure cap therefor includes a screw-threaded part having a thread profile with a step in that ank of the thread which trails as the thread is screwed up, the thread prole being such that, when the part is screwed onto a cooperating thread of conventional prole, the crest of the conventional thread has a clearance at the root of the thread on the screwthreaded part, and the step being shaped so that as the two threads are tightened and there is an axial thrust between them, the crest of the conventional thread is forced onto the step which has an interference lit with the crest of the conventional thread so that the two threads are frictionally held tightly against release.

In the particular case of a bottle with an externally screw-threaded neck and a cap with an internally threaded skirt, the thread having a profile with a step in its ank is preferably provided on the cap, which may be moulded out of flexible plastics material and the thread on the neck of the bottle is then of conventional design. Thus in this case, the cap has a skirt with an internal thread having a prole `with a step in the flank of the thread remote from the open end of the skirt, the thread profile being such 3,480,170 Patented Nov. 25, 1969 that when the cap is screwed onto a conventional thread on the neck of :a bottle, the crest of the bottle thread has a clearance at the root of the cap thread, and the step being shaped so that as the cap is tightened on the bottle, and there is an axial thrust between the neck of the bottle and the cap, the crest of the bottle thread is forced onto the step which has an interference t Iwith the crest of the bottle thread so that the cap is frictionallyheld tightly against release.

Where, as an alternative, however, the cap is provided with a conventional thread, the thread on the bottle neck has a thread prole with a step in the ank remote from the open end of the neck. The thread profile is such and the step is so shaped that the same action takes place as when the stepped thread is on the cap.

In either case, to enable the crest of the conventional thread to ride onto the step, some degree of resilience is necessary in the bottle or the cap and the amount of interference provided between the crest of the conventional thread and the step is dependent upon the degree of resilience. When the crest of the conventional thread is on the step, a radical thrust is exerted between the two and therefore the frictional resistance encountered when the cap is to be unscrewed is greater than that encountered with a normal screw cap. To remove the cap from the bottle, the cap must be unscrewed to such an extent that there is suicient axial play between the cap and the bottle to allow the cap to be moved on the bottle to force the crest of the conventional thread off the step back towards the root of the stepped thread Iwhere there is a clearance. After this has been done, the cap can easily be unscrewed in the same way as a normal cap provided with ya clearance over the whole of its thread profile, but until the crest of the conventional thread can be forced from the step the frictional resistance which opposes the unscrewing of the cap continues while the cap is unscrewed whereas with a conventional screw cap, once the initial resistance is overcome the cap is at once loose.

With a container or cap having a thread in accordance with the invention, a child will not only nd the cap hard to turn from its fully screwed up position, but the child must continue to turn the cap for some distance against the frictional resisting torque before the cap can be loosened and removed. Therefore even though a child may be able to produce instantaneously the necessary torque to move the cap, it is unlikely that the child would be able to produce this torque for sufficient time to loosen the cap completely,

Apart from this resistance to unscrewing which provides a child safety characteristic, however, a part, and in particular a bottle or cap, provided with a thread in accordance with the present invention has an advantage which is capable of even more widespread use than applications where a degree of resistance to opening by children is necessary. Thus, owing to the inaccuracies which necessarily occur in the production of screwthreads on bottles or moulded caps, it is necessary with conventional threads to provide a tolerance which gives rise to a substantial clearance between the thread on the bottle and thread on the cap. As the conventional threads are screwed up or unscrewed, the cap be displaced radially on the bottle neck in such a way that there is no clearance between the cap and bottle threads at one side of the bottle but a substantial clearance at the other side. If there is any resilience, as is usually the case with caps moulded out of plastic-s material, especially thermoplastic material, there is a tendency for the thread to deilect locally at the point of maximum clearance as the cap is screwed up on the bottle and what is known as peeling of the thread may then take place. This means that the thread on the bottle and thread on the cap ride over each other at the point of deflection of the cap thread so that the thread is no longer effective in anchoring the cap in position on the bottle.

In order to prevent this happening, it is necessary to make the skirt of the cap of sutcient rigidity to prevent the local deflection of the thread, which gives rise to thread peeling, from taking place. This makes it necessary to make the skirt of the cap thicker than is necessary from other considerations of the strength of the cap.

When either the cap or the bottle is provided with a stepped thread in accordance with the present invention, however, although there may be a substantial clearance between the crest of the conventional thread and the root of the stepped thread to allow for normal manufacturing tolerances, it is possible for there to be a substantial interference between the step and the crest of the conventional thread -so that even allowing for tolerances there is still some interference. Thus as the crest of the conventional thread starts to ride onto the shoulder, there is no clearance at all at any point around the cap and the neck of the bottle. There is thus continuous line contact between the two threads and owing to this lack of clearance the cap is automatically centred on the bottle neck. Because there is no excessive clearance at any one point, so that the thread on the skirt of the bottle cap is supported all the way round, there is no possibility of any local deformation of this thread taking place. Thread peeling cannot therefore occur and it is possible to make the skirt of the bottl-e cap of very much thinner material than would otherwise be possible whilst still ensuring that the thread securely anchors the cap in position on the bottle.

This feature is of particular importance with bottle caps made of polypropylene and other quite flexible thermoplastic materials and it enable caps to be made of these materials with very such thinner sections than would otherwise be possible. Since a considerable proportion of the total cost of a cap lies in the cost of the material from which it is made, there is an extremely worthwhile overall reduction in the cost of the cap.

A still further advantage of the self-locking thread is that is greatly assists in resisting backing off which is an inherent tendency existing with all screw-threaded closures to come loose with cibration. The tendency is a result of the axial locking force which exists between the two threads and the helix angle of the threads which together tend to unscrew the closure. Backing olf my occur when the compression of parts of a closure or of a wad within the closure relaxes or the container and its closure is subjected to vibration such as is experienced in transit.

The face of the step onto which the crest of the conventional thread is forced when the two threads are fully tightened together may be concave so that the crest of the conventional thread ts into the step to some extent. That is to say in the locked position, the step engages over and extends beyond the crest of the conventional thread. In this case, as the two threads are unscrewed, the crest of the conventional thread will remain on the step and to release it, not only must the two threads be unscrewed from each other suiciently, but the two threads must be pressed axially to force the crest of the conventional thread off the step. In the case of a bottle and cap, the cap must be unscrewed and then pressed downwards onto the bottle until the conventional thread snaps free into the clearance around the root of the step thread. In the case of bottles for pharmaceutical products and other materials which must be kept out of the reach of children, the shaping of the step in this way provides added safety since most children would not follow the sequence of actions consisting of unscrewing the cap and then pressing it downwards, their nautral tendency bein-g to pull the cap off rather than to push it down as they unscrew it.

If on the other hand the step is flat in an axial direction so that it does not extend in engagement with the conventional thread beyond the crest of the conventional thread, the conventional thread will tend to jump olf the step as soon as the two threads have been unscrewed sufficiently.

. An example of a screw-threaded cap and of a container constructed in accordance with the invention are illustrated in the accompanying drawings in which:

FIGURE l is a diametric section through a bottle cap in accordance with the invention shown in the course of being screwed onto a bottle neck provided with a conventional thread;

FIGURE 2 is a diametric section similar to FIGURE l, but showing the cap at a later stage of its being screwed onto the neck;

FIGURE 3 is a section similar to FIGURES 1 and 2, but showing the cap screwed fully onto the neck of the bottle;

FIGURE 4 is a perspective view to a smaller scale of the cap shown in FIGURES l to 3;

,FIGURE 5 is a side elevation of the neck of a bottle in accordance with the invention with a cap, shown in diametric section, in the course of being screwed onto the bottle neck; and,

FIGURE 6 is a view similar to FIGURE 5, but showing the cap screwed fully onto the bottle neck.

In the example illustrated in FIGURES 1 to 4 of the drawings, a glass bottle 1 has a neck 2 provided with a thread 3 of a conventional rounded profile.

A closure cap 4, which in this example, is made of polypropylene by injection moulding, but may be made by compression moulding, has a top wall 5 and a skirt 6. The cap is injection moulded out of polypropylene. Inside the inner end of the skirt 6 is a resilient sealing wad 7 and the outside peripheral surface 8 of the skirt 6 is provided with a series of axially extending ribs to enable it to be firmly gripped.

The skirt 6 is provided with an internal screw-thread 9, the profile of which has a straight root section 10 and also a straight leading ank 11 which is the flank which is on the side of the thread adjacent the open end of the skirt 6.

The other ank of the thread 9, that is the ank adjacent the top wall 5 of the cap has a straight portion 12 and a step 13. The step 13 is concave as seen in radial section in FIGURES l to 3 of the drawings and extends from the edge of the straight portion 12 up to a crest 14.

The diameter of the root 10 is such that it has a substantial clearance around the crest of the thread 3, but the diameter of the radially outermost part of the step 13 is such that even allowing for manufacturing tolerances, it has an interference lit with the crest of the thread 3. Thus, as the cap 4 is initially screwed onto the neck 2, the crest 14 rides on the uppermost ank of the thread 3 and there is a clearance between the crest of the thread 3 and the root 10 and also between the crest 14 and the root of the thread 3.

As screwing on of the cap 4 continues, an end face 15 of the neck 2 comes into Contact with the underside of the wad 7 so that there is an upward axial thrust applied to the cap 4 by the neck 2. This causes the thread 9 to ride up towards the thread 3 until the position shown in FIG- URE 2 of the drawings is reached. Here, a corner 16 of the step 13 has come into contact with the thread 3 just below its crest.

As screwing on of the cap 4 continues, the wad 7 is further compressed and the axial force between the neck 2 and the cap 4 increases until the crest of the thread 3 is forced onto the step 13 around the whole extent of the two threads as is shown in FIGURE 3 of the drawings.

When this stage is reached, the cap 4 is held screwed onto the neck 2 not only by the frictional force generated by the axial thrust between the threads 3 and 9, which is dependent upon the screwing on torque applied to the cap 4, but also by the frictional force generated by a radial thrust between the step 13 and the crest of the thread 3, This radial thrust is determined by the amount of interference between the step 13 and the crest of the thread 3 and is independent of the torque applied to the cap 4 to screw it on, provided that this is suflicient to force the crest of the thread 3 up onto the step 13.

As the cap 4 is unscrewed again, the frictional torque resisting unscrewing provided by the axial thrust between the neck 2 and the cap 4 immediately decreases and falls to Zero as soon as the wad 7 is no longer compressed. However, the crest of the thread 3 remains on the step 13 s0 that the friction brought about by the radial force between the threads persists and this continues until the cap 4 has been unscrewed sufficiently far to enable the cap 4 to be pressed downwards and cause the crest of the thread 3 to be moved off the step 13.

To assist in tightening and unscrewing the cap 4, this is provided with a pair of parallel ribs 17 projecting upwards from its top wall 5 to enable a coin shown irl chain-dotted lines at 18 in FIGURE 4 to be inserted be tween the ribs and act like a screw driver.

In the example shown in FIGURES 5 and 6 of the drawings, a bottle 21 has a neck 22 provided with a screwthread 23. A cap 24 has a top wall 25 with a skirt 26 and an internal wad 27. The bottle including the thread on the neck is made by a conventional technique, for example extrusion/ blow-moulding or injection/ blow-moulding when made of thermoplastic material or parison blowmoulding when made of glass.

In this example, the skirt 26 has an internal thread 29 of conventional prole with straight anks 30 and a straight crest 31. The thread 23 has a straight ank 32 on the side of the thread adjacent the open end of the neck 22 and a ank on its side remote from the open end of the neck which has a straight portion 33 adjacent its crest 34 and a step 35 leading to a straight portion 36 adjacent its root 37.

The crest of the thread 29 has a clearance around the root 37, but is an interference fit with the step 35.

As the cap 24 is first screwed on, the threads adopt the positions shown in FIGURE 5 of the drawings in which the crest 34 rides on the lowermost flank 30 of the thread 29.

As the cap 24 is tightened, however, and there is an axial thrust between the wad 27 and an end surface 38 on the neck 22, the thread 29 is forced to ride upon to the thread 23 through a position corresponding to the position shown in FIGURE 2 of the drawing into a fully locked position shown in FIGURE 6 of the drawings in which the crest 31 is forced onto the steps 35.

Under these conditions, there is a radial thrust between the threads 23 and 29 which produces a locking torque in exactly the same way as in the example illustrated in FIGURES 1 to 4. This locking torque persists on unscrewing the cap 24 until it is possible to push the cap downwards relatively to the neck 22 so that the crest 31 is pushed olf the step 35.

In the example shown in FIGURES 5 and 6 the cap 24 may, of course, if desired be provided with ribs similar to the ribs 17 in the example illustrated -in FIGURES 1 to 4 or with other means for facilitating screwing up and unscrewing the cap.

We claim:

1. In a container or closure therefor including a screwthreaded part, a screw-thread having a thread profile including a root, two flanks and a step in that one of said flanks of said thread which trails as said thread is screwed up, said thread profile being such that when said part is screwed onto a cooperating thread of conventional prole including a crest, said crest of said conventional thread has a clearance at said root of said thread on said screw-threaded part, and said step being so shaped whereby as said thread on said screw-threaded part and said conventional thread are tightened to generate an axial thrust between said threads, said thrust forces said crest of said conventional thread onto said step, said step having an interference t with said crest of said conventional thread whereby said two threads are frictionally held tightly against release.

2. A bottle closure cap including an end wall, a skirt depending from said wall, said skirt having an open end, and an internal screw-thread on said skirt, said internal screw-thread having a thread profile including a root, two flanks and a step in that one of said two anks of said thread which is remote from said open end of said skirt, said thread prole being such that when said cap is screwed onto a cooperating thread of conventional prole including a crest on a bottle neck, said crest of said conventional thread has a clearance at said root of said internal thread and said step being so shaped whereby as said internal thread and said conventional thread are tightened to generate an axial thrust between said threads, said thrust forces said crest of said conventional thread onto said step, said step having an interference t with said crest of said conventional thread whereby said cap is frictionally held on said bottle tightly against release.

3. A bottle having a neck having an open end and an external screw-thread on said neck, said external screwthread having a thread profile including a root, two flanks and a step in that one of said two flanks of said thread which is remote from said open end of said neck, said thread prole being such that when a cap including a cooperating thread of conventional profile including a crest is screwed onto said neck, said crest of said conv entional thread has a clearance at said root of said external thread, and said step being so shaped whereby as said external thread and said conventional thread are tightened to generate an axial thrust between said threads, said thrust forces said crest of `said conventional thread onto said step, said step having an interference t with said crest of said conventional thread whereby said cap is frictionally held on said bottle tightly against release.

4. A container or closure therefor as claimed in claim 1, wherein said step includes a concave face onto which said crest of said conventional thread is forced, whereby said crest lits into said step and said step engages over and extends beyond said crest of said conventional thread.

5. A cap as claimed in claim 2, further comprising a keying device on said top wall for engagement of an implement to facilitate turning said cap.

6. A cap as claimed in claim 2, wherein said step onto which said crest of said conventional thread is forced is concave whereby said crest ts into said step and said step engages over and extends beyond said crest of said conventional thread.

References Cited UNITED STATES PATENTS GEORGE T. HALL, Primary Examiner U.S. Cl. X.R. 21S- 9; 220-39 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION 3,1480 ,170 Dated November 25, 1969 TREVOR GWILYM EVANS and GEOFFREY ALAN RYDER Patent No.

Inventor-(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Michael James [73] Assignee:

welwyn Garden City,

England Signed and sealed this lith day of June 1971+.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attestng Officer Commissioner of Patents 

